1. Field of the Invention
The present invention relates to surface treating methods of titanium parts. Moreover, the present invention relates to engine valves that are treated by utilizing such surface treating methods.
2. Description of the Related Art
A surface treating method of a titanium part is taught, for example, by Japanese Laid-open Patent Publication Number 11-117056, in which the titanium part is oxidized in order to produce a wear resistant hard oxide film on its surface. In this known art, an engine valve made from a metastable β titanium alloy is exemplified as the titanium part, because it has been generally known that when an α-β titanium alloy is oxidized, its fatigue strength is reduced.
In addition, it has been conventionally believed that thicker oxide films (e.g., more than 30 micrometer) are more appropriate than thinner oxide films.